feat: add source fact ledger and repository hygiene CI

[amnotyoung]

Summary

• add a pre-scoring source-fact ledger with stable F IDs and an early ledger-only gate
• preserve F/X traceability through detailed ratings, conflict registers, and report composition
• add Git-inventory-based CI for copy-suffix, portable path, canonical ID, and duplicate body collisions
• keep v0.12.0 immutable; these changes remain under Unreleased

Validation

• 88 Python regression tests passed
• 15 Boulder hook tests passed
• repository hygiene: 108 Git-target files, 0 collisions
• manifest sync, mirror audit, plugin validation, and evaluate/write-report skill validation passed
• clean ledger-only and full auditable-brief fixtures passed